Competitive Interactions Between Palatable and Unpalatable Grasses: Effects of Selective Defoliations of the Palatable Grasses

Selective herbivory of the palatable species appears to be a dominant mechanisms contributing to species competitive replacement in grasslands. Selective herbivory of the palatable species allows unpalatable species to realize a competitive advantage within the community. To test this hypothesis we compare the competitive ability of the unpalatable grasses Stipa trichotoma or S. gyneriodes in the presence of nondefoliated and defoliated plants of the palatable grass S. clarazii. The three species are native to a temperate semiarid grassland of Argentina. The response variables estimated in S.trichotoma and S.gynerioides, at both plant and tiller levels, were higher (P \u3c 0.05) in the presence of defoliated than in the presence of undefoliated plants of S.clarazii. These results support the hypothesis that selective herbivory of the palatable species confers unpalatable species a competitive advantages, contributing to species competitive replacement within the community

Replicative Acinetobacter baumannii strains interfere with phagosomal maturation by modulating the vacuolar pH

Bacterial pneumonia is a common infection of the lower respiratory tract that can afflict patients of all ages. Multidrug-resistant strains of Acinetobacter baumannii are increasingly responsible for causing nosocomial pneumonias, thus posing an urgent threat. Alveolar macrophages play a critical role in overcoming respiratory infections caused by this pathogen. Recently, we and others have shown that new clinical isolates of A. baumannii, but not the common lab strain ATCC 19606 (19606), can persist and replicate in macrophages within spacious vacuoles that we called Acinetobacter Containing Vacuoles (ACV). In this work, we demonstrate that the modern A. baumannii clinical isolate 398, but not the lab strain 19606, can infect alveolar macrophages and produce ACVs in vivo in a murine pneumonia model. Both strains initially interact with the macrophage endocytic pathway, as indicated by EEA1 and LAMP1 markers; however, the fate of these strains diverges at a later stage. While 19606 is eliminated in an autophagy pathway, 398 replicates in ACVs and are not degraded. We show that 398 reverts the natural acidification of the phagosome by secreting large amounts of ammonia, a by-product of amino acid catabolism. We propose that this ability to survive within macrophages may be critical for the persistence of clinical A. baumannii isolates in the lung during a respiratory infection

Modern Acinetobacter baumannii clinical isolates replicate inside spacious vacuoles and egress from macrophages

Multidrug-resistant Acinetobacter baumannii infections are increasing at alarming rates. Therefore, novel antibiotic-sparing treatments to combat these A. baumannii infections are urgently needed. The development of these interventions would benefit from a better understanding of this bacterium\u27s pathobiology, which remains poorly understood. A. baumannii is regarded as an extracellular opportunistic pathogen. However, research on Acinetobacter has largely focused on common lab strains, such as ATCC 19606, that have been isolated several decades ago. These strains exhibit reduced virulence when compared to recently isolated clinical strains. In this work, we demonstrate that, unlike ATCC 19606, several modern A. baumannii clinical isolates, including the recent clinical urinary isolate UPAB1, persist and replicate inside macrophages within spacious vacuoles. We show that intracellular replication of UPAB1 is dependent on a functional type I secretion system (T1SS) and pAB5, a large conjugative plasmid that controls the expression of several chromosomally-encoded genes. Finally, we show that UPAB1 escapes from the infected macrophages by a lytic process. To our knowledge, this is the first report of intracellular growth and replication of A. baumannii. We suggest that intracellular replication within macrophages may contribute to evasion of the immune response, dissemination, and antibiotic tolerance of A. baumannii

Ecological succession of a Jurassic shallow-water ichthyosaur fall.

After the discovery of whale fall communities in modern oceans, it has been hypothesized that during the Mesozoic the carcasses of marine reptiles created similar habitats supporting long-lived and specialized animal communities. Here, we report a fully documented ichthyosaur fall community, from a Late Jurassic shelf setting, and reconstruct the ecological succession of its micro- and macrofauna. The early 'mobile-scavenger' and 'enrichment-opportunist' stages were not succeeded by a 'sulphophilic stage' characterized by chemosynthetic molluscs, but instead the bones were colonized by microbial mats that attracted echinoids and other mat-grazing invertebrates. Abundant cemented suspension feeders indicate a well-developed 'reef stage' with prolonged exposure and colonization of the bones prior to final burial, unlike in modern whale falls where organisms such as the ubiquitous bone-eating worm Osedax rapidly destroy the skeleton. Shallow-water ichthyosaur falls thus fulfilled similar ecological roles to shallow whale falls, and did not support specialized chemosynthetic communities

Role of the dynein/dynactin motor complex of the host cell in the biogenesis of the vacuole containing Coxiella burnetii

En el trasporte retrógrado participa el complejo motor dineína/dinactina. Coxiella burnetii (Cb) es un patógeno intracelular obligado que transita a través de la vía fagocítica para formar la vacuola replicativa que contiene a Cb (VCC). Existe poca evidencia acerca de la interrelación entre el tráfico intracelular de Cb y proteínas motoras. Para estudiar esa interrelación se analizó la sobreexpresión de las formas WT de las subunidades del complejo motor dineína/dinactina, y la sobreexpresión de las mutantes no funcionales respectivas, alterando la formación de la VCC. Nuestros resultados sugieren que los fagosomas que contienen C. burnetii, se transportan utilizando dineína/dinactina para formar la VCC, donde Cb se multiplica.In the retrograde transport, the dynein/dynactin motor complex is involved. Coxiella burnetii (Cb) is an obligate intracellular pathogen that transits through the phagocytic pathway to form the replicative vacuole containing Cb (VCC). There is little evidence about the interrelationship between intracellular Cb trafficking and motor proteins. To study this interrelation, we analysed the overexpression of the WT forms of the dynein/dynactin motor complex subunits, and overexpression of the respective non-functional mutants, altering the formation of the VCC. Our results suggest that C. burnetiicontaining phagosomes are transported using dynein/ dinactin to form the VCC, where Cb is multiplied.Fil: Ortiz Flores, Rodolfo M.. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histologia y Embriología Mendoza. "Dr. Mario H. Burgos"Fil: Distel, Jesús S.. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histologia y Embriología Mendoza. "Dr. Mario H. Burgos"Fil: Aguilera, Milton O.. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histologia y Embriología Mendoza. "Dr. Mario H. Burgos"Fil: Berón, Walter. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Instituto de Histologia y Embriología Mendoza. "Dr. Mario H. Burgos

Evolutionarily stable gene clusters shed light on the common grounds of pathogenicity in the Acinetobacter calcoaceticus-baumannii complex

Nosocomial pathogens of the Acinetobacter calcoaceticus-baumannii (ACB) complex are a cautionary example for the world-wide spread of multi- and pan-drug resistant bacteria. Aiding the urgent demand for novel therapeutic targets, comparative genomics studies between pathogens and their apathogenic relatives shed light on the genetic basis of human-pathogen interaction. Yet, existing studies are limited in taxonomic scope, sensing of the phylogenetic signal, and resolution by largely analyzing genes independent of their organization in functional gene clusters. Here, we explored more than 3,000 Acinetobacter genomes in a phylogenomic framework integrating orthology-based phylogenetic profiling and microsynteny conservation analyses. We delineate gene clusters in the type strain A. baumannii ATCC 19606 whose evolutionary conservation indicates a functional integration of the subsumed genes. These evolutionarily stable gene clusters (ESGCs) reveal metabolic pathways, transcriptional regulators residing next to their targets but also tie together sub-clusters with distinct functions to form higher-order functional modules. We shortlisted 150 ESGCs that either co-emerged with the pathogenic ACB clade or are preferentially found therein. They provide a high-resolution picture of genetic and functional changes that coincide with the manifestation of the pathogenic phenotype in the ACB clade. Key innovations are the remodeling of the regulatory-effector cascade connecting LuxR/LuxI quorum sensing via an intermediate messenger to biofilm formation, the extension of micronutrient scavenging systems, and the increase of metabolic flexibility by exploiting carbon sources that are provided by the human host. We could show experimentally that only members of the ACB clade use kynurenine as a sole carbon and energy source, a substance produced by humans to fine-tune the antimicrobial innate immune response. In summary, this study provides a rich and unbiased set of novel testable hypotheses on how pathogenic Acinetobacter interact with and ultimately infect their human host. It is a comprehensive resource for future research into novel therapeutic strategies.Peer Reviewe

Evolutionarily stable gene clusters shed light on the common grounds of pathogenicity in the Acinetobacter calcoaceticus-baumannii complex

Nosocomial pathogens of the Acinetobacter calcoaceticus-baumannii (ACB) complex are a cautionary example for the world-wide spread of multi- and pan-drug resistant bacteria. Aiding the urgent demand for novel therapeutic targets, comparative genomics studies between pathogens and their apathogenic relatives shed light on the genetic basis of human-pathogen interaction. Yet, existing studies are limited in taxonomic scope, sensing of the phylogenetic signal, and resolution by largely analyzing genes independent of their organization in functional gene clusters. Here, we explored more than 3,000 Acinetobacter genomes in a phylogenomic framework integrating orthology-based phylogenetic profiling and microsynteny conservation analyses. We delineate gene clusters in the type strain A. baumannii ATCC 19606 whose evolutionary conservation indicates a functional integration of the subsumed genes. These evolutionarily stable gene clusters (ESGCs) reveal metabolic pathways, transcriptional regulators residing next to their targets but also tie together sub-clusters with distinct functions to form higher-order functional modules. We shortlisted 150 ESGCs that either co-emerged with the pathogenic ACB clade or are preferentially found therein. They provide a high-resolution picture of genetic and functional changes that coincide with the manifestation of the pathogenic phenotype in the ACB clade. Key innovations are the remodeling of the regulatory-effector cascade connecting LuxR/LuxI quorum sensing via an intermediate messenger to biofilm formation, the extension of micronutrient scavenging systems, and the increase of metabolic flexibility by exploiting carbon sources that are provided by the human host. We could show experimentally that only members of the ACB clade use kynurenine as a sole carbon and energy source, a substance produced by humans to fine-tune the antimicrobial innate immune response. In summary, this study provides a rich and unbiased set of novel testable hypotheses on how pathogenic Acinetobacter interact with and ultimately infect their human host. It is a comprehensive resource for future research into novel therapeutic strategies

RATA: A method for high-throughput identification of RNA bound transcription factors.

Long non-coding RNAs (lncRNAs) regulate critical cellular processes and their dysregulation contributes to multiple diseases. Although only a few lncRNAs have defined mechanisms, many of these characterized lncRNAs interact with transcription factors to regulate gene expression, suggesting a common mechanism of action. Identifying RNA-bound transcription factors is especially challenging due to inefficient RNA immunoprecipitation and low abundance of many transcription factors. Here we describe a highly sensitive, user-friendly, and inexpensive technique called RATA (RNA-associated transcription factor array), which utilizes a MS2-aptamer pulldown strategy coupled with transcription factor activation arrays for identification of transcription factors associated with a nuclear RNA of interest. RATA requires only ~5 million cells and standard molecular biology reagents for multiplexed identification of up to 96 transcription factors in 2-3 d. Thus, RATA offers significant advantages over other technologies for analysis of RNA-transcription factor interactions